Measuring viscosity with Honeybun just got cooler

Importance of the topic

Viscosity is a critical quality attribute in the development of biologic therapeutics at every stage from discovery through manufacturing to administration. High viscosities can signal protein–protein interactions, aggregation, or denaturation under refrigerated conditions, while in later development they challenge filtration, fill–finish operations, and subcutaneous injection performance. Reliable, low-volume, rapid viscosity measurement over a wide temperature range is therefore essential for formulation screening, stability assessment, and process optimization.

Objectives and Overview of the study

This study evaluates Honeybun, a microvolume viscometer and rheometer designed for protein, vaccine, viral vector, and injectable formulations. The goals were to demonstrate its accuracy and precision across a dynamic range of 0.5–150 cP at temperatures from 4 to 45 °C, to compare measurements against predicted viscosities for glycerol–water mixtures, and to apply the system to high-concentration monoclonal antibody solutions to define injectability thresholds.

Methodology

• Preparation of aqueous glycerol solutions at 0, 70, 75, 77, and 78% w/w and measurement in 20 replicates each at 4 °C using 35 µL default mode on Honeybun.
  
• Formulation of two monoclonal antibodies at 170 mg/mL in 10 mM histidine buffer; verification of concentration, hydrodynamic diameter, and polydispersity via Stunner.
  
• Viscosity measurements of mAb solutions in default (35 µL) and low-volume (15 µL) modes at five temperatures between 4 and 40 °C, each in triplicate.
  

Used Instrumentation

• Honeybun microvolume viscometer/rheometer with disposable Bun consumables (35 µL default, 15 µL low-volume).
  
• Unagi dilution system for preparation of antibody solutions.
  
• Stunner instrument for particle size and concentration verification.
  

Results and Discussion

Viscosity measurements of glycerol–water standards closely matched predicted values (e.g., 150 cP target vs. 157.4 ± 5.8 cP measured), with water at 1.567 cP predicted vs. 1.56 ± 0.03 cP measured. Precision and accuracy were maintained across the full 0.5–150 cP range at 4 °C.

For both mAb1 and mAb2 at 170 mg/mL, viscosity decreased nonlinearly with increasing temperature, following an approximately logarithmic trend. mAb1 exhibited consistently higher viscosity than mAb2, indicating stronger protein–protein interactions and higher aggregation risk. Based on a comfort threshold of 20 cP for subcutaneous injection, mAb1 would require temperatures above ~28 °C, while mAb2 could be injected above ~13 °C.

Default and low-volume modes produced indistinguishable results, confirming the reliability of measurements down to 15 µL of sample.

Benefits and Practical Applications

Honeybun delivers rapid throughput (up to 10 samples in under a minute for low-viscosity, under 10 minutes for high-viscosity), minimal sample consumption, factory calibration, and hands-free operation without extensive cleaning or calibration steps. This enables high-throughput formulation screening, stability monitoring, manufacturability assessment, and injectable formulation development in discovery, process development, and quality control labs.

Future Trends and Applications

• Integration with predictive modelling and AI to forecast viscosity behavior from formulation parameters.
  
• Automation and higher density parallel measurement for large-scale formulation libraries.
  
• Expansion of temperature and rheological measurement modes for advanced biotherapeutic characterization.
  
• On-line or at-line process monitoring for real-time viscosity control in manufacturing.
  

Conclusion

Honeybun provides accurate, precise, and rapid viscosity measurement of biological formulations over a broad dynamic range and temperature span using minimal sample volumes. Its ease of use, throughput, and reliability make it a valuable tool for accelerating biologic development, ensuring manufacturability, and optimizing injection performance.

References

1. Shire SJ. Challenges in the subcutaneous (SC) administration of monoclonal antibodies (mAbs). Monoclonal Antibodies. 2015:131–138.
   
2. Berteau C et al. Evaluation of the impact of viscosity, injection volume, and injection flow rate on subcutaneous injection tolerance. Medical Devices (Auckland, NZ). 2015;8:473–484.
   
3. Cheng N-S. Formula for the Viscosity of a Glycerol−Water Mixture. Ind Eng Chem Res. 2008;47(9):3285–3288.
   
4. Hong T et al. Viscosity Control of Protein Solution by Small Solutes: A Review. Curr Protein Pept Sci. 2017;19(8):746–758.